The coupling of HCHO, though generally run under mild conditions, is difficult to control, often leading to low/poor selectivity to GA (eq. 1). Competing reactions to form GlyAld, C4 and higher sugars (eq. 2), and dihydroxyacetone (DHA), from the aldol condensation of HCHO and GA (eq. 3), contribute to the low selectivity that is generally observed.
1. Condensation of HCHO to glycoaldehyde

2. Condensation of formaldehyde and glycoaldehyde to C3 and higher sugars

3. Aldol Condensation of formaldehyde and glycoaldehyde

Numerous examples exist in the prior art in which both homogeneous and heterogeneous catalysts have been used to carry out the coupling of HCHO to form GA. The following citations can be used as examples of the existing art in this field: A. H. Weiss, U.S. Pat. No. 4,238,418; J. H. Teles et al., U.S. Pat. Nos. 5,585,496, 5,298,668 and 5,508,422; and J. H. Teles et al. Helvetica Chimica Acta 1996, 79, 61.
GA is an attractive C2 material as a precursor to ethylene glycol (EG). The formose reaction provides a simple reaction utilizing formaldehyde as a relatively inexpensive source for making a C2 compound, if the selectivity to C2 can be controlled. GA could then be hydrogenated under relatively mild hydrogenation conditions to EG, an attractive alternative to the known routes using extreme pressures and temperatures (GB 508, 383; U.S. Pat. No. 2,153,064).
Homogeneous triazolium salts, imidazolium salts and thiazolium salts have been used as catalysts for the self-condensation of formaldehyde to GA. The reactions are run under moderate temperatures and ambient pressure, with yields approaching 70% with the triazolium salts as catalysts. In most cases, a significant amount of C3 and higher sugars are seen. In the case of the imidazolium salts, almost no GA is observed (see Teles et al.) with the major product in these reactions being DHA and very poor yields. Low conversion of the HCHO to product can be attributed to the coupling of the imidazolium carbene catalysts used in the reactions, a problem which has been addressed in this invention.
In order to minimize the by-products, a catalyst is needed that selectively makes the C2 GA and does not allow subsequent coupling to occur either by controlling the active site on the catalyst or optimizing the reaction conditions.